Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H→invisible decays where H is produced ...according to the standard model via vector boson fusion, Z(ℓℓ)H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 fb^{-1} of pp collisions at a center-of-mass energy of sqrts=13 TeV at the LHC. In combination with the results at sqrts=7 and 8 TeV, an exclusion limit on the H→invisible branching ratio of 0.26(0.17_{-0.05}^{+0.07}) at 95% confidence level is observed (expected).
Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose ...data-collection rates at low transverse momentum are much lower than the rate from standard model multijet production. This Letter describes a new search for dijet resonances where this limitation is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs. The search targets low-mass dijet resonances in the range 450–1800 GeV. The analyzed data set has an integrated luminosity of up to 29.3 fb−1 and was recorded at a center-of-mass energy of 13 TeV. No excesses are found; limits are set on Gaussian-shaped contributions to the dijet mass distribution from new particles and on a model of dark-matter particles with axial-vector couplings to quarks.
A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton–proton collisions at a centre-of-mass energy of 13
TeV
by the ATLAS detector at the ...Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb
-
1
. Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain
b
-hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for local excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical
Z
′
bosons, Kaluza–Kein gluons and Kaluza–Klein gravitons that decay into top-quark pairs.
Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W±W∓ or ZZ pairs ...from a decay of a dark Higgs boson s is searched for using 139 fb−1 of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The s→V(q¯q)V(q¯q) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with ms>160 GeV are excluded.
Abstract In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from ...the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of $^{3}\overline{{{\rm{He}}}$$ 3 He ¯ when it encounters matter particles and annihilates or disintegrates within the ALICE detector at the Large Hadron Collider. We extract the inelastic interaction cross section, which is then used as an input to the calculations of the transparency of our Galaxy to the propagation of $^{3}\overline{{{\rm{He}}}$$ 3 He ¯ stemming from dark-matter annihilation and cosmic-ray interactions within the interstellar medium. For a specific dark-matter profile, we estimate a transparency of about 50%, whereas it varies with increasing $^{3}\overline{{{\rm{He}}}$$ 3 He ¯ momentum from 25% to 90% for cosmic-ray sources. The results indicate that $^{3}\overline{{{\rm{He}}}$$ 3 He ¯ nuclei can travel long distances in the Galaxy, and can be used to study cosmic-ray interactions and dark-matter annihilation.
The upcoming GAMMA-400 experiment will be implemented aboard the Russian astrophysical space observatory, which will be operating in a highly elliptical orbit over a period of 7 years to provide new ...data on gamma-ray emissions and cosmic-ray electron + positron fluxes, mainly from the galactic plane, the Galactic Center, and the Sun. The main observation mode will be a continuous point-source mode, with a duration of up to ~100 days. The GAMMA-400 gamma-ray telescope will study high-energy gamma-ray emissions of up to several TeV and cosmic-ray electrons + positrons up to 20 TeV. The GAMMA-400 telescope will have a high angular resolution, high energy and time resolutions, and a very good separation efficiency for separating gamma rays from the cosmic-ray background and the electrons + positrons from protons. A distinctive feature of the GAMMA-400 gamma-ray telescope is its wonderful angular resolution for energies of >30 GeV (0.01° for Eγ = 100 GeV), which exceeds the resolutions of space-based and ground-based gamma-ray telescopes by a factor of 5–10. GAMMA-400 studies can reveal gamma-ray emissions from dark matter particles’ annihilation or decay, identify many unassociated, discrete sources, explore the extended sources’ structures, and improve the cosmic-ray electron + positron spectra data for energies of >30 GeV.
In a simple thermodynamic model, transverse momentum distributions are found for
-hyperons produced in pp collisions at ultrarelativistic energies. Studying the behavior of the average transverse ...momentum depending on the mass of the emitted particle shows that it is possible to search for large mass quark nuggets as possible candidates for the role of dark matter particles. An interpretation of the spectra of soft photons with respect to the transverse momentum in pp collisions is also given taking into account the boson X17, a new particle, a possible candidate for the role of dark matter particles.
We study the determination of the symmetry that stabilizes a dark matter (DM) candidate produced at colliders. Our question is motivated per se, and by several alternative symmetries that appear in ...models that provide a DM particle. To this end, we devise a strategy to determine whether a heavy mother particle decays into one visible massless particle and one or two DM particles. The counting of DM particles in these decays is relevant to distinguish the minimal choice of Z2 from a Z3 stabilization symmetry, under which the heavy particle and the DM are charged and the visible particle is not. Our method is novel in that it chiefly uses the peak of the energy spectrum of the visible particle and only secondarily uses the MT2 endpoint of events in which the heavy mother particles are pair-produced. We present new theoretical results concerning the energy distribution of the decay products of a three-body decay, which are crucial for our method. To demonstrate the feasibility of our method in investigating the stabilization symmetry, we apply it in distinguishing the decay of a bottom quark partner into a b quark and one or two DM particles. The method can be applied generally to distinguish two- and three-body decays, irrespective of DM.
Exploring Low-Mass Dark Matter with CRESST Strauss, R.; Angloher, G.; Bento, A. ...
Journal of low temperature physics,
08/2016, Letnik:
184, Številka:
3-4
Journal Article
Recenzirano
Odprti dostop
The CRESST-II (Cryogenic Rare Event Search with Superconducting Thermometers) experiment, whose second phase has been successfully finished in summer 2015, aims at the direct detection of dark matter ...particles. The intrinsic radiopurity of CaWO
4
crystals, the capability to reject recoil events from alpha-surface contamination, and the energy threshold were significantly improved compared to previous runs of the experiment. A moderate exposure of 29 kg-days acquired by one
∼
250 g CaWO
4
detector provides competitive limits on the spin-independent dark matter particle-nucleon cross section and probes a new region of parameter space for dark matter particle masses below 3 GeV/c
2
. The potential for low-mass dark matter particle search can be further exploited by a new detector design planned for CRESST-III. We describe the experimental strategy for the near future and give projections for the sensitivity.
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